// callback 表示回調(diào)函數(shù)，deps是依賴數(shù)組，下同
function mountCallback(callback, deps) {
 // 調(diào)用 mountWorkInProgress方法創(chuàng)建新的hook，并將其放到fiber的memoizedState鏈表上，最后返回新的hook
  const hook = mountWorkInProgressHook();
  // 判斷依賴，若不存在，則為null
  const nextDeps = deps === undefined ? null : deps;
  // 將callback和deps 存放到fiber.memoizedState中，以便后續(xù)復(fù)用
  hook.memoizedState = [callback, nextDeps];
  // 最后返回callback
  return callback;
}

function updateCallback(callback, deps) {
  // 調(diào)用updateWorkInProgressHook讀取舊Fiber的對(duì)應(yīng)舊hook，以及復(fù)用舊hook，創(chuàng)建新hook并返回
  const hook = updateWorkInProgressHook();
  // 新的依賴取值
  const nextDeps = deps === undefined ? null : deps;
  // 從新hook上取hook之前數(shù)據(jù)
  const prevState = hook.memoizedState;
  // 若新依賴不等于null
  if (nextDeps !== null) {
    const prevDeps = prevState[1];
    // 則判斷新舊依賴是否發(fā)生了改變
    if (areHookInputsEqual(nextDeps, prevDeps)) {
    // 若沒變化，則直接返回之前的callback
      return prevState[0];
    }
  }
  // 若新依賴不存在，或者新舊依賴不等，則再次將callback和deps依賴存入到fiber中
  hook.memoizedState = [callback, nextDeps];
  // 返回callback
  return callback;
}

function mountMemo(
  nextCreate,
  deps,
): T {
  const hook = mountWorkInProgressHook();
  const nextDeps = deps === undefined ? null : deps;
  const nextValue = nextCreate();
  hook.memoizedState = [nextValue, nextDeps];
  return nextValue;
}
function updateMemo(
  nextCreate,
  deps,
) {
  const hook = updateWorkInProgressHook();
  const nextDeps = deps === undefined ? null : deps;
  const prevState = hook.memoizedState;
  if (nextDeps !== null) {
    const prevDeps = prevState[1];
    if (areHookInputsEqual(nextDeps, prevDeps)) {
      return prevState[0];
    }
  }
  const nextValue = nextCreate();
  hook.memoizedState = [nextValue, nextDeps];
  return nextValue;
}